The research interests of the Cleveland group focus on mechanisms of neuronal growth and death using molecular genetics to assess how axons grow and what factors provoke selective death of motor neurons. Unlike most eukaryotic cells, an intrinsic feature of neurons is their extreme asymmetry. for example, in the human peripheral nervous system, single motor neurons extend over a meter in length. Asymmetry is achieved in two phases. The first is when a neurite extends towards its target. After stable synapse formation, a second phase initiates in which the axon grows up to ten fold in diameter. This radial growth phase, concomitant with meylination and essential for establishment of proper conduction velocity, yields an enormous increase in axonal volume and a huge cell, 99.9% of which is in the axon. We have focused part of our effort on using molecular genetics and transgenic mice to test how radial growth of axons is achieved. Already we have shown that neurofilaments, the most abundant structural element in axons, are essential for radial growth. We have now identified a set of neurofilament-associated proteins and, in collaboration with Dr. Burlingame, now wish to use modern protein analysis methods to determine the identities of these associated proteins. Once the corresponding genes are isolated we will then use transgenic and gene disruption methods in mice to determine the corresponding in vivo properties. Beyond this, essentially all human motor neuron disorders are characterized by the maldistribution of neurofilaments, a finding clearly suggesting that they may play an essential role in disease pathogenesis. This is particularly true in the most prominent motor neuron disease, amyotrophic lateral sclerosis, or ALS, which is characterized by selective death of motor neurons. By producing transgenic mice expressing mutations in neurofilaments, we have proven that such mutations can cause ALS in mice and we are now searching for the presence of similar mutations in human patients. The cause of only 1.5% of human ALS is known and this is point mutations in an enzyme superoxide dismutase. By expression of these mutations in mice, we have proven that disease arises from a toxic property of the mutant proteins and we are now looking for what that property is and what is the cascade of events leading to selective motor neuron death. By using high resolution protein analysis methods, we now seek to determine whether neurofilaments are indeed targets for covalent damage arising from ALS-linked SOD1 mutations, and if so, to identify the nature of the aberrant chemistry mediated by these mutant proteins.